Method for producing polymer coated pigment particles by precipitation

ABSTRACT

Described is a process for preparing polymer-enrobed pigment particles, which comprises mixing in the presence of finely dispersed pigment particles a solution of a polymer in a first solvent with a second solvent in which the polymer is substantially insoluble. The pigment particle can be specifically modified by judicious selection of the polymer.

DESCRIPTION

The present invention relates to a process for producing polymer-enrobedpigment particles, to the pigment preparations thus produced and to theuse thereof.

Pigments and disperse dyes are important water-insoluble colorants. Formaximum color strength and brilliance, they frequently need to be in acolloidally disperse state comprising a small particle size and narrowparticle size distribution. Pigments and disperse dyes have to bestabilized against agglomeration and flocculation. The colloidallydisperse state is particularly important in injket printing for example,a widely used process for the contactless printing of various printmedia.

WO 99/51695 describes precipitated water-insoluble dyes in colloidallydisperse form having an average particle size from 5 nm to 1 μm andhaving a variance of less than 50%. The dye particles are precipitatedin the colloidally disperse form by adding water to the solution of thedye in a solvent. The water preferably contains a protective colloid,i.e., a water-soluble natural or synthetic homo- or copolymer.

DE 198 45 078 A1 concerns dye-containing polymer particles containing atleast one dye in a matrix of an essentially water-insoluble polymer andhaving an average particle size in the range from 5 to 500 nm and aparticle size distribution width (variance) of ≦35%. The dye-containingpolymer particles are precipitated from a solution which contains thedye and a water-insoluble polymer in a water-miscible organic solvent.

WO 99/40123 discloses a process for preparing dye-containing aqueouspolymer dispersions by free-radical aqueous emulsion polymerization ofethylenically unsaturated monomers, which comprises at least some of themonomers being employed in the form of an oil-in-water emulsion whosedisperse phase contains at least one oil-soluble dye and is formedessentially by dye-containing monomer droplets having a diameter of lessthan 500 nm.

The aforementioned publications all describe processes using dispersedyes or oil-soluble dyes. It has been determined that the colorantsproduced according to the above prior art are insufficiently lightfastand migration-stable. The migration of dyes constitutes a problemespecially when printing on textiles owing to the different affinitiesof the various dyes for various fabrics, particularly blend fabrics.

U.S. Pat. No. 4,665,107 concerns a process for modifying pigmentparticles by encapsulation with polymeric starting materials. Ahomogeneous dispersion consisting of primary pigment particles andpolymer in a substantially water-immiscible organic solvent is dispersedin water to form an emulsion. The solvent is then distilled off and theemulsion droplets convert into solid particles. This process isdisadvantageous in that the fine dispersion of a liquid in another istechnically far from straightforward, even with the use of emulsifiers.Moreover, the dispersed droplets have a tendency to coalesce, since itis only the distillative removal of the solvent which gives rise to theencapsulated pigment particles. Furthermore, generally more than onepigment particle is present in the emulsion droplet and in the colorantparticle obtained therefrom. For maximum brilliance and color strengthideally only one pigment particle should be encapsulated.

It is an object of the present invention to provide a simple process forproducing lightfast, waterfast and migration-stable colorantpreparations comprising colloidally disperse colorants and a preferablynarrow particle size.

We have found that this object is achieved by a process in which finelydivided pigments are enrobed with polymers by precipitating the polymerfrom a solution in the presence of finely divided pigment particles.Pigments exhibit excellent lightfastness and migration stability.

The present invention accordingly provides a process for preparingpolymer-enrobed pigment particles, which comprises mixing in thepresence of finely dispersed pigment particles a solution of a polymerin a first solvent with a second solvent in which the polymer issubstantially insoluble and which is miscible with the first solvent.

The pigment particles may be present in fine dispersion in the solutionof the polymer in the first solvent and/or in the second solvent priorto the mixing. Alternatively the pigment particles may be initiallycharged as a dispersion whose dispersion medium is identical to, say,the first solvent.

The process may be continuously as well as batch operated. Mixing ispreferably effected under turbulent conditions. Useful apparatuses forthe mixing, especially the turbulent mixing, of two liquids are known toone skilled in the art and include for example stirred tanks, Y- orT-tubes, which are optionally equipped with static mixers, or mixingnozzles.

The choice of the first solvent depends on the solubility of the polymerused. The first solvent is preferably a water-miscible organic solvent.Water-miscible solvents for the purposes of the present inventioninclude solvents having miscibility gaps with water. In these cases, theamount ratios are chosen so that miscibility is ensured. Generally, theyshould be at least 10% by weight water-miscible. Examples of suitablesolvents include mono- and polyalcohols such as methanol, ethanol,n-propanol, isopropanol, glycol, glycerol, propylene glycol,polyethylene glycol; also ethers such as tetrahydrofuran, dioxane,1,2-propanediol 1-n-propyl ether, 1,2-butanediol 1-methyl ether,ethylene glycol monomethyl ether, diethylene glycol monomethyl ether;esters such as methyl acetate, monoesters of ethylene glycol orpropylene glycols with acetic acid, butyrolactone; ketones such asacetone or methyl ethyl ketone; amides such as formamide,dimethylformamide, dimethylacetamide, N-methylpyrrolidone andhexamethylphosphoramide; sulfoxides and sulfones such as dimethylsulfoxide and sulfolane; alkanecarboxylic acids such as formic acid oracetic acid.

Particularly preferred first solvents are methanol, acetone,tetrahydrofuran and dimethylformamide.

The second solvent is preferably water.

In the individual case, both the first and the second solvent areorganic solvents, for example toluene or cyclohexane as the firstsolvent and methanol or diisopropyl ether as the second solvent.

The weight ratio of first solvent to second solvent is generally in therange from 2:1 to 1:50, especially in the range from 1:4 to 1:10. Whenthe second solvent is water, it is generally used in excess over thefirst solvent. If desired, the pH of the aqueous phase may be adjustedto a desired value.

The dissolving of the polymer and also the mixing of the aqueous phasewith the organic solvent phase are customarily effected in the rangefrom room temperature to the boiling point of the solvent. The reactionis preferably carried out at atmospheric pressure, although it is alsopossible to employ superatmospheric pressure.

Useful pigments include not only finely divided organic but alsoinorganic pigments and also mixtures thereof.

Useful inorganic pigments include:

-   -   white pigments        -   such as titanium dioxide (C.I. Pigment White 6), zinc white,            color zinc oxide; lead white; zinc sulfide, lithopone;    -   black pigments        -   such as carbon black (C.I. Pigment Black 7); iron manganese            black, spinel black (C.I. Pigment Black 27), iron oxide            black (C.I. Pigment Black 11);    -   color pigments        -   such as chromium oxide, chromium oxide hydrate green; chrome            green (C.I. Pigment Green 48); cobalt green (C.I. Pigment            Green 50); ultramarine green; cobalt blue (C.I. Pigment Blue            28 and 36); ultramarine blue; iron blue (C.I. Pigment Blue            27); manganese blue; ultramarine violet; cobalt and            manganese violet; iron oxide red (C.I. Pigment Red 101);            cadmium sulfoselenide (C.I. Pigment Red 108); molybdate red            (C.I. Pigment Red 104); ultramarine red; iron oxide brown,            mixed brown, spinel and corundum phases (C.I. Pigment Brown            24, 29 and 31), chrome orange; iron oxide yellow (C.I.            Pigment Yellow 42); nickel titanium yellow (C.I. Pigment            Yellow 53); C.I. Pigment Yellow 157 and 164; chromium            titanium yellow; cadmium sulfide and cadmium zinc sulfide            (C.I. Pigment Yellow 37 and 35); chrome yellow (C.I. Pigment            Yellow 34), zinc yellow, alkaline earth metal chromates,            Naples yellow; bismuth vanadate (C.I. Pigment Yellow 184);    -   interference pigments        -   metal effect pigments, pearl luster pigments;    -   fillers and/or delusterants        -   such as SiO₂ (Aerosil R 812), precipitated CaCO₃;    -   magnetic pigments        -   such as CrO₂, Fe₂O₃, Fe₃O₄, cobalt-modified iron oxides,            barium ferrites, pure iron pigments;

useful organic pigments from the Colour Index list are:

-   -   monoazo pigments        -   C.I. Pigment Brown 25;        -   C.I. Pigment Orange 5, 13, 36 and 67;        -   C.I. Pigment Red 1, 2, 3, 5, 8, 9, 12, 17, 22, 23, 31, 48:1,            48:2, 48:3, 48:4, 49, 49:1, 52:1, 52:2, 53, 53:1, 53:3,            57:1, 251, 112, 146, 170, 184, 210 and 245;        -   C.I. Pigment Yellow 1, 3, 73, 74, 65, 97, 151 and 183.    -   diazo pigments        -   C.I. Pigment Orange 16, 34 and 44;        -   C.I. Pigment Red 144, 166, 214 and 242;        -   C.I. Pigment Yellow 12, 13, 14, 16, 17, 81, 83, 106, 113,            126, 127, 155, 174, 176 and 188;    -   anthanthrone pigments        -   C.I. Pigment Red 168 (C.I. Vat Orange 3);    -   anthraquinone pigments        -   C.I. Pigment Yellow 147 and 177;        -   C.I. Pigment Violet 31;    -   anthrapyrimidine pigments        -   C.I. Pigment Yellow 108 (C.I. Vat Yellow 20);    -   quinacridone pigments        -   C.I. Pigment Red 122, 202 and 206; C.I. Pigment Violet 19;    -   quinophthalone pigments        -   C.I. Pigment Yellow 138;    -   dioxazine pigments        -   C.I. Pigment Violet 23 and 37;    -   flavanthrone pigments        -   C.I. Pigment Yellow 24 (C.I. Vat Yellow 1);    -   indanthrone pigments        -   C.I. Pigment Blue 60 (C.I. Vat Blue 4) and 64 (C.I. Vat Blue            6);    -   isoindoline pigments        -   C.I. Pigment Orange 69; C.I. Pigment Red 260; C.I. Pigment            Yellow 139 and 185;    -   isoindolinone pigments        -   C.I. Pigment Orange 61; C.I. Pigment Red 257 and 260; C.I.            Pigment Yellow 109, 110, 173 and 185;    -   isoviolanthrone pigments        -   C.I. Pigment Violet 31 (C.I. Vat Violet 1);    -   metal complex pigments        -   C.I. Pigment Yellow 117 and 153; C.I. Pigment Green 8;    -   perinone pigments        -   C.I. Pigment Orange 43 (C.I. Vat Orange 7); C.I. Pigment Red            194 (C.I. Vat Red 15);    -   perylene pigments        -   C.I. Pigment Black 31 and 32; C.I. Pigment Red 123, 149,            178, 179 (C.I. Vat Red 23), 190 (C.I. Vat Red 29) and 224;            C.I. Pigment Violet 29;    -   phthalocyanine pigments        -   C.I. Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6 and 16;        -   C.I. Pigment Green 7 and 36;    -   pyranthrone pigments        -   C.I. Pigment Orange 51, C.I. Pigment Red 216 (C.I. Vat            Orange 4);    -   thioindigo pigments        -   C.I. Pigment Red 88 and 181 (C.I. Vat Red 1); C.I. Pigment            Violet 38 (C.I. Vat Violet 3);    -   triarylcarbonium pigments        -   C.I. Pigment Blue 1, 61 and 62; C.I. Pigment Green 1; C.I.            Pigment Red 81, 81:1 and 169; C.I. Pigment Violet 1, 2, 3            and 27;    -   C.I. Pigment Black 1 (aniline black);    -   C.I. Pigment Yellow 101 (aldazine yellow);    -   C.I. Pigment Brown 22;        vat dyes (other than those already mentioned above):    -   C.I. Vat Yellow 2, 3, 4, 5, 9, 10, 12, 22, 26, 33, 37, 46, 48,        49 and 50;    -   C.I. Vat Orange 1, 2, 5, 9, 11, 13, 15, 19, 26, 29, 30 and 31;    -   C.I. Vat Red 2, 10, 12, 13, 14, 16, 19, 21, 31, 32, 37, 41, 51,        52 and 61;    -   C.I. Vat Violet 2, 9, 13, 14, 15, 17 and 21;    -   C.I. Vat Blue 1 (C.I. Pigment Blue 66), 3, 5, 10, 12, 13, 14,        16, 17, 18, 19, 20, 22, 25, 26, 29, 30, 31, 35, 41, 42, 43, 64,        65, 66, 72 and 74;    -   C.I. Vat Green 1, 2, 3, 5, 7, 8, 9, 13, 14, 17, 26, 29, 30, 31,        32, 33, 40, 42, 43, 44 and 49;    -   C.I. Vat Brown 1, 3, 4, 5, 6, 9, 11, 17, 25, 32, 33, 35, 38, 39,        41, 42, 44, 45, 49, 50, 55, 57, 68, 72, 73, 80, 81, 82, 83 and        84;    -   C.I. Vat Black 1, 2, 7, 8, 9, 13, 14, 16, 19, 20, 22, 25, 27,        28, 29, 30, 31, 32, 34, 36, 56, 57, 58, 63, 64 and 65.

Preferred pigments are SiO₂ (Aerosil), Pigment Blue 15:4, Pigment Blue15:3, Pigment Red 122 and Pigment Yellow 138.

The pigment should be very finely divided. The pigment particlespreferably have a particle size ≦1 μm, especially in the range from 0.01μm to 0.5 μm.

The weight ratio of pigment particles to total amount of the first andsecond solvents is customarily in the range from 1:20 to 1:10,000,preferably about 1:1000 to 1:5000.

The process of the invention is notable for the multiplicity of polymerswhich can be used. Mixtures of polymers can also be used. The thermalproperties, such as the glass transition temperature or the meltingpoint, and the mechanical and optical properties, such as the refractiveindex, of the particles can be optimized to the end use. Judiciouschoice of the polymer makes it possible to modify, especiallyhydrophilicize or hydrophobicize, the surfaces of the pigment particles.

Each or every polymer has to be soluble in the first solvent andsubstantially insoluble in the second solvent. Generally, the solubilityof the polymer in the second solvent is less than 1 g/l in order thatthe losses of polymer may be minimized. The solubility of the polymer inthe first solvent is customarily at least 10 g/l in order that thevolumes of liquid may be kept small. The concentration of the polymerdissolved in the first solvent is customarily about 10 g/l to 40 g/l,especially from 10 g/l to 25 g/l. The term “polymer” as used herein alsocomprehends a mixture of various polymers.

The polymer is directly precipitated when its solubility is exceeded inthe course of the turbulent mixing of the two solvents. It ispredominantly or completely precipitated onto the pigment particles andeffectively encapsulates them.

Useful polymers include first of all polyesters. They are preparable ina simple manner by condensation polymerization of aliphatic,cycloaliphatic and aromatic di-, tri- and/or polycarboxylic acids ortheir functional derivatives such as anhydrides or chlorides with di-,tri- and/or polyols. Useful carboxylic acids include for exampledicarboxylic acids of 2 to 20 carbon atoms, preferably 4 to 15 carbonatoms, for example malonic acid, succinic acid, glutaric acid, adipicacid, pimelic acid, suberic acid, sebacic acid, dodecanedioic acid,phthalic acid, terephthalic acid, isophthalic acid,cyclohexanedicarboxylic acid, etc. Useful carboxylic acids furtherinclude sulfosuccinic acid and sulfoisophthalic acid. Dicarboxylic acidsmay be used individually or as mixtures. Useful diols include forexample glycols, preferably glycols of 2 to 25 carbon atoms. Usefulglycols include for example 1,2-ethanediol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol,diethylene glycol, 2,2,4-trimethyl-1,5-pentanediol,2,2-dimethyl-1,3-propanediol, 1,4-dimethylolcyclohexane,1,6-dimethylolcyclohexane and ethoxylated/propoxylated products of2,2-bis(4-hydroxyphenyl)-propane (bisphenol A), etc. Branched andcrosslinked polyesters are formed in the polycondensation of trihydricor higher alcohols with polyfunctional carboxylic acids. Useful triolsand polyols have for example 3 to 25, preferably 3 to 18 carbon atoms.These include for example glycerol, trimethylolpropane, erythritol,pentaerythritol, sorbitol and alkoxylates thereof, etc.

The polycondensation of hydroxycarboxylic acids or lactones leads topolyesters of the hydroxycarboxylic acid type. These consist of just onemonomer, the hydroxycarboxylic acid. Useful hydroxycarboxylic acidsinclude α-hydroxycarboxylic acids such as glycolic acid, lactic acid,hydroxybutyric acid, mandeleic acid, which may each also be present inthe form of its lactides, or β-hydroxycarboxylic acids,γ-hydroxycarboxylic acids, δ-hydroxycarboxylic acids andω-hydroxycarboxylic acids respectively. Useful lactones for preparingpolyesterols include for example lactones of 3 to 20 carbon atoms, suchas α,α-dimethyl-β-propiolactone, γ-butyrolactone, ε-caprolactone, etc.

Useful polyesters further include polycarbonates, i.e., polyesters ofcarbonic acid with hydroxy compounds. Their properties can be variedwithin wide limits in the synthesis by judicious choice of the dihydroxycompound, which can be aliphatic or aromatic or a mixture thereof. Aparticularly suitable polycarbonate is Lexan 141, which is marketed byGE Plastics.

Useful polymers further include polyvinyl acetals, such as polyvinylformals or polyvinyl butyrals, which are available by reaction ofpolyvinyl alcohol with aldehydes such as formaldehyde or butyraldehyde,and also polyacetals, such as polyoxymethylene in particular.

Useful polymers for the process of the invention further includepolyurethanes and polyureas. They are formed for example in thepolyaddition of diols or diamines with diisocyanates. Usefuldiisocyanates include for example diisocyanates such as hexamethylenediisocyanate, isophorone diisocyanate, phenylene 1,4-diisocyanate,naphthylene 1,5-diisocyanate or toluylene 2,4- or 2,6-diisocyanate. Thediol may be of low molecular weight, for example ethylene glycol,propylene glycol, 1,4-butylene glycol, etc., or polymeric such as, forexample, a polyester- or polyetherdiol.

Useful polymers further include homo- or copolymers of ethylenicallyunsaturated monomers. The copolymers may be random copolymers, blockcopolymers, graft copolymers and the like. Useful polymers consist of10-100% by weight, preferably 20-90% by weight, of one or morewater-insoluble ethylenically unsaturated monomers, 0-90% by weight,preferably 5-80% by weight, of one or more water-soluble ethylenicallyunsaturated monomers and 0-30% by weight, preferably 2-20% by weight, ofone or more crosslinking monomers.

Useful water-insoluble ethylenically unsaturated monomers include:

-   i) esters of α,β-ethylenically unsaturated C₃-C₈-monocarboxylic    acids and C₄-C₈-dicarboxylic acids with C₁-C₁₂-alkanols, especially    C₁-C₈-alkanols. Examples of these mono- and dicarboxylic acids    include acrylic acid, methacrylic acid, crotonic acid, maleic acid,    fumaric acid, itaconic acid and citraconic acid, of which acrylic    acid and methacrylic acid are preferred. Examples of C₁-C₁₂-alkanols    include methanol, ethanol, n-propanol, i-propanol, n-butanol,    i-butanol, sec-butanol, t-butanol, 2-ethylhexanol, n-octanol and    n-dodecanol. Preferred esters include methyl methacrylate, n-butyl    acrylate and 2-ethylhexyl acrylate;-   ii) vinyl esters of C₁-C₁₂-monocarboxylic acids, especially    C₁-C₈-monocarboxylic acids. Examples of vinyl esters include vinyl    acetate, vinyl propionate, vinyl butyrate, vinyl hexanoate and vinyl    decanoate;-   iii) styrenics, such as styrene and α-methylstyrene;-   iv) C₂-C₆-olefins, such as ethylene, propene, 1-butene, 2-butene and    isobutene or diolefins having conjugated double bonds, such as    butadiene or isoprene.-   v) acrylonitrile, methacrylonitrile; vinyl ethers of C₁-C₈-alkanols,    especially vinyl ethyl ether.

Useful water-soluble ethylenically unsaturated monomers include monomershaving polar groups, i.e., anionic monomers, cationic monomers andnonionic monomers. They generally have a water solubility of at least 5g/l at 25° C. A monomer is termed water soluble even when its ionized,i.e., protonated or deprotonated, form meets the specified solubilitycriterion.

Anionic monomers are preferably selected from:

-   i) α,β-ethylenically unsaturated C₃-C₈-monocarboxylic acids and    C₄-C₈-dicarboxylic acids and the monoesters with C₁-C₁₂-alkanols and    the anhydrides thereof. Examples of these carboxylic acids are    indicated above as acid component of the esters. Acrylic acid and    methacrylic acid are preferred;-   ii) aromatic vinylcarboxylic acids, such as 2-, 3- or 4-vinylbenzoic    acid;-   iii) monoethylenically unsaturated sulfonic and phosphonic acids,    such as vinylsulfonic acid, allylsulfonic acid, vinylbenzenesulfonic    acid, vinylphosphonic acid.

Particularly preferred anionic monomers include acrylic acid,methacrylic acid and vinylsulfonic acid.

Useful cationic monomers include ethylenically unsaturatedbasic-nitrogen compounds. Preference is given to esters of theabove-described α,β-ethylenically unsaturated C₃-C₈-monocarboxylic acidswith amino-C₂-C₈-alkanols, mono-C₁-C₄-alkylamino-C₂-C₈-alkanols ordi-C₁-C₄-alkylamino-C₂-C₈-alkanols, N-vinylimidazoles and 2-, 3- or4-vinylpyridines and the quaternary forms thereof obtained by alkylationwith alkyl halides, dialkyl sulfates and alkylene oxides.

Preferred nonionic water-soluble monomers include N-vinyllactams,especially N-vinylpyrrolidone, esters of α,β-ethylenically unsaturatedC₃-C₈-monocarboxylic acids with C₂-C₄-alkanediols and the ethoxylated orpropoxylated derivatives thereof, amides, mono-C₁-C₄-alkylamides anddi-C₁-C₄-alkylamides of the above-recited α,β-ethylenically unsaturatedC₃-C₈-monocarboxylic acids, preferably acrylamide and methacrylamide.

Crosslinking monomers are polyfunctional monomers having two or morenonconjugated ethylenically unsaturated bonds or containing an alkoxy,hydroxyl or N-alkylol group as well as an ethylenically unsaturatedbond. Examples thereof include the diesters of dihydric alcohols withthe abovementioned ethylenically unsaturated monocarboxylic acids, thevinyl and allyl esters of ethylenically unsaturated carboxylic acids oraromatic divinyl compounds, especially ethylene glycol diacrylate,1,4-butylene glycol diacrylate, propylene glycol diacrylate, vinylmethacrylate, allyl acrylate and divinylbenzene. Examples ofpolyfunctional monomers include the N-hydroxyalkylamides andN-alkylolamides of the ethylenically unsaturated carboxylic acidsmentioned and also glycidyl acrylate and glycidyl methacrylate.

Useful examples of homo- or copolymers of ethylenically unsaturatedmonomers include polystyrene and copolymers of styrene such as ASA, SAN,ABS; a terpolymer of styrene, acrylic acid and 4-vinylpyridine;polyvinyl acetate and also polymethyl methacrylate.

The amount ratio of pigment to polymer is generally in the range from1:0.1 to 1:10 parts by weight, preferably in the range from 1:0.5 to 1:7parts by weight.

The first and/or second solvents preferably contain an emulsifier and/ora protective colloid. They may further contain customary assistants suchas humectants and preservatives. Alternatively the dispersion of thepolymer-enrobed pigment particles may also be admixed therewith in oneor more downstream process steps. The downstream process step may becontinuously as well as batch operated.

The second solvent, especially when it is water, preferably contains atleast one protective colloid. The presence of the protective colloidensures long-term stabilization by preventing the agglomeration of thecolloidally disperse particles. Advantageously the first and/or secondsolvent(s) additionally contain(s) at least one emulsifier.

Useful protective colloids include the natural or semisynthetic polymerscustomarily used for this purpose. Useful natural or semisyntheticprotective colloids include for example gelatin, including fish gelatin,starch or starch derivatives, such as dextrins, pectin, gum arabic,caseine, caseinate, alginates, cellulose and cellulose derivatives suchas methylcellulose, carboxymethylcellulose, hydroxypropylcellulose orhydroxypropylmethylcellulose. Sodium caseinate is used in particular.

Useful synthetic protective colloids include water-soluble homo- orcopolymers, which may be neutral polymers, cationic polymers or anionicpolymers. Complexes of polycationic and polyanionic polymers and alsocoacervates may also be used.

The protective colloid polymers are polymerized from monomers havinghydrophilic groups and optionally comonomers having hydrophobic groups,the ratio between hydrophilic and hydrophobic groups being chosen sothat the copolymer is water soluble.

Useful hydrophilic monomers include for example N-vinyllactams, such asN-vinylpyrrolidone; acrylamide or methacrylamide and their N-C₁-C₄-mono-or N,N-di-C₁-C₄-alkyl derivatives; acrylic acid or methacrylic acid;monomers having a primary, secondary or tertiary basic nitrogen atomsuch as amino-C₂-C₄-alkyl acrylates and methacrylates, for exampledimethylaminoethyl (meth)acrylate, and the derivatives thereofquaternized with C₁-C₄-alkylating agents; ethylenically unsaturatedsulfonic acids such as vinylsulfonic acid, acrylamido-N-propanesulfonicacid and styrenesulfonic acid; hydroxy-C₂-C₄-alkyl acrylates andmethacrylates; allyl alcohol and methallyl alcohol; olefinicallyunsaturated compounds having epoxy groups such as glycidyl acrylate andglycidyl methacrylate; monoesters and diesters of ethylenicallyunsaturated C₄-C₈-dicarboxylic acids such as maleic acid and itaconicacid with aminoalcohols such as dimethylaminoethanol; and amides orimides of these carboxylic acids with diamines such asdimethylaminopropylamine.

Useful comonomers having hydrophobic groups include for exampleC₂-C₄-alkyl vinyl ethers such as ethyl vinyl ether; vinyl esters ofC₂-C₈-carboxylic acids such as vinyl acetate and vinyl propionate;C₁-C₈-alkyl acrylates and methacrylates such as methyl, ethyl, n-butyland 2-ethylhexyl acrylate and methacrylate; styrenics such as styrene;and α-olefins having up to 20 carbon atoms such as ethylene, propyleneand isobutylene.

The amount of protective colloid in the second solvent is generally inthe range from 1 to 50% by weight, preferably in the range from 3 to 30%by weight, based on the total weight of the respective phase.

Emulsifiers are stabilizing assistants. They are also known assurfactants. Useful emulsifiers include the customary emulsifiers usefulfor preparing emulsions. The emulsifiers may be anionic, cationic ornonionic in nature. Anionic emulsifiers include for example soaps,alkanesulfonates, olefinsulfonates, alkylarylsulfonates,alkylnaphthalenesulfonates, sulfosuccinates, alkyl sulfates and alkylether sulfates, alkyl methyl ester sulfates, acyl glutamates,sarcosinates and taurates. Examples include sodium laurylsulfate, sodiumlauryl ether sulfate, oleylsulfonate, nonylbenzenesulfonate, sodiumdodecylbenzenesulfonate and butylnaphthalenesulfonate.

Cationic emulsifiers include for example alkyltrimethylammoniumhalides/alkylsulfates, alkylpyridinium halides anddialkyldimethylammonium halides/alkylsulfates.

Useful nonionic emulsifiers include for example alkoxylatedanimal/vegetable fats and oils, for example corn oil ethoxylates, castoroil ethoxylates, tallow fat ethoxylates; glyceryl esters, for exampleglyceryl monostearate; fatty alcohol alkoxylates and oxo alcoholalkoxylates; alkylphenol alkoxylates, for example isononylphenolethoxylates; and sugar surfactants, for example sorbitan fatty acidesters (sorbitan monooleate, sorbitan tristearate), polyoxyethylenesorbitan fatty acid ester.

It is also possible to use zwitterionic emulsifiers, such assulfobetaines, carboxybetaines, alkyldimethylamine oxides, for exampletetradecyldimethylamine oxide, and polymer surfactants, such as di-,tri- and multi-block polymers of the type (AB)x, ABA and BAB, forexample polyethylene oxide-block-polypropylene oxide,polystyrene-block-polyethylene oxide and AB comb polymers, for examplepolymethacrylate-comb-polyethylene oxide.

Another useful emulsifier is the ethoxylated and sulfonated bisphenol Aadduct with styrene.

Useful emulsifiers further include fluorosurfactants. Their hydrophobicgroup is a fluoro- or perfluoroalkyl radical, especially aC₈-C₂₂-perfluoroalkyl radical. They further contain a hydrophilic group,usually a carboxylate, sulfonate or sulfate group. They are effective inextremely low concentrations, which are substantially lower than in thecase of conventional surfactants. They are also notable for highchemical and thermal stability. Preference is given to using the BayowetFT 448 fluorosurfactant marketed by Bayer.

The amount of emulsifier in the first and/or second solvents isgenerally in the range from 10 to 500% by weight, preferably in therange from 50 to 200% by weight, based on the total weight of thepigment used.

The aqueous phase preferably contains a humectant such as1,2-propanediol or glycerol.

The aqueous phase preferably contains a preservative such as for examplea 1,2-benzisothiazoline compound.

The pigment dispersion obtained by the process of the invention is usedeither directly or after admixture with assistants and additivescustomary in these cases, provided these had not already been dissolvedin the first and/or second solvents prior to precipitation. Customaryassistants and additives include for example viscosity modifiers such aswater-soluble starch and cellulose derivatives as thickeners.

Alternatively the colorant preparation may be concentrated in aconventional manner, for example by evaporating off the first solventwith or without a portion of the second solvent. Volatiles may also beremoved completely, for example by spray drying. The dyes of theinvention are obtained in the form of a dry powder which isredispersible, for example in water. Further protective colloids may beadded before or during the concentrating in order that even bettercolloidal stabilization may be obtained.

The polymer-enrobed pigment particles generally have an average particlesize in the range from 10 nm to 5 μm and a particle size distributionwidth (variance) of ≦60%. The particle size is suitably measured byquasi-elastic light scattering and evaluated by the cumulant method (seeBruce, J. Berne and Robert Pecora, “Dynamic Light Scattering”, JohnWiley & Sons Inc. 1976, p. 196). The average particle size is preferablyin the range from 5 nm to 1 μm and the width of the particle sizedistribution is preferably ≦50%.

The process of production is such that the polymer-enrobed pigmentparticle will generally contain only one pigment particle as core. Thepigment serves as a seed onto which the polymer is precipitated.

The invention also provides a pigment preparation, for example in theform of an inkjet ink preparation, containing the pigment particlesencapsulated according to the invention, usually in an aqueous phase.

The pigment preparations of the invention are very useful for printingprint media, especially for printing paper, foil, film, papers for thereproduction of digital photographic images and graphics and also forprinting textiles. The preferred process for printing textiles istransfer printing.

Pigment preparations of the invention can be waterfast if awater-insoluble polymer is used for enrobing the pigment particles.Thus, aqueous pigment dispersions can be finished with water-insolublepolymers which are lightfast and migration stable.

In the inkjet printing process, the aqueous colorant preparation issprayed in small droplets directly onto the substrate. There is acontinuous form of the inkjet process, in which the colorant preparationis uniformly pressed through a nozzle and the jet is directed onto thesubstrate by an electric field depending on the pattern to be printed,and there is an interrupted or drop-on-demand process, in which the inkis expelled only where a colored dot is to appear, the latter form ofthe process employing either a piezoelectric crystal or a heated cannula(bubble or thermal jet process) to exert pressure on the ink system andso eject an ink droplet. These techniques are described in Text. Chem.Color, Vol. 19(8), p. 23-29, 1987, and Vol. 21(6), p. 27-32, 1989.

The colorant preparations used according to the invention may be printedon all types of substrate material. Useful substrate materials includefor example

-   -   coated or uncoated cellulosics such as paper, paperboard,        cardboard, wood and woodbase,    -   coated or uncoated metallic materials such as foils, sheets or        workpieces composed of aluminum, iron, copper, silver, gold,        zinc or alloys thereof,    -   coated or uncoated silicatic materials such as glass, porcelain        and ceramics,    -   polymeric materials of any kind such as polystyrene, polyamides,        polyesters, polyethylene, polypropylene, melamine resins,        polyacrylates, polyacrylonitrile, polyurethanes, polycarbonates,        polyvinyl chloride, polyvinyl alcohols, polyvinyl acetates,        polyvinylpyrrolidones and corresponding copolymers and block        copolymers, biodegradable polymers and natural polymers such as        gelatin,    -   textile materials such as fibers, yarns, threads, knits, wovens,        nonwovens and garments composed of polyester, modified        polyester, polyester blend fabrics, cellulosics such as cotton,        cotton blend fabrics, jute, flax, hemp and ramie, viscose, wool,        silk, polyamide, polyamide blend fabrics, polyacrylonitrile,        triacetate, acetate, polycarbonate, polypropylene, polyvinyl        chloride, polyester microfibers and glass fiber fabrics,    -   leather—both natural and artificial—in the form of smooth        leather, nappa leather or suede leather.

Alternatively, the images and patterns created by inkjet printing mayfirst be applied to an intermediate substrate, for example a transferpaper, and applied to a second substrate, for example a textilesubstrate, by contacting the latter. This process frequently takes placeat elevated temperature, for example at from 180 to 200° C., in a press.

The print created on the substrate may be fixed using a heat treatmentfor example. This succeeds particularly when the pigment particles havebeen enrobed with thermoplastic polymers having a glass transitiontemperature of −100 to +250° C., especially from 0 to 220° C., moreparticularly from 20 to 200° C. Fixation thus requires only relativelylow temperatures, as generated for example by ironing or by means ofsome other heat source, for the polymer matrix to flow and to form a dyefilm on the substrate, for example a textile.

Alternatively or additionally the print can be fixed by subsequentlyapplying a binder, if desired in the form of an aqueous dispersion oremulsion, and cured. Radiation-curable, thermally curable or air dryingbinders or physically drying binder dispersions or emulsions may beused. Examples of radiation-curable binders are monomers, prepolymers,polymers and blends thereof that contain acrylate groups, vinyl groupsand/or epoxy groups.

Thermally curable binders are generally crosslinked via polycondensationor polyaddition reactions. Particularly useful thermally curable bindersinclude for example polycondensation-crosslinking binders based onacrylates containing methylol groups.

Examples of air drying binders, where aliphatic double bonds areoxidatively crosslinked by the action of oxygen from air, are dryingoils such as linseed oil, wood oil and safflower oil.

Further examples of applications for the pigment preparations of theinvention include the coloring of polymer compositions such aspolyethylene (HDPE, LPPE), polyurethane and styrene acrylonitrile.

Because the pigment particles have been modified by enrobement with apolymer, the pigments are easy to incorporate in and compatibilize withthe polymer compositions to be colored.

The examples which follow illustrate the invention. They exemplify theprecipitation of a polymer dissolved in a water-miscible organic solventby mixing with an aqueous phase.

In Examples 1-4 the pigment is present as a dispersion in the aqueousphase. In Example 5 an aqueous pigment dispersion is stirred into thepolymer solution immediately prior to the mixing with the rest of theaqueous phase.

In Examples 6 and 7 the polymer solution contains the dispersed pigment.In Example 8 the pigment is present as a dispersion in the aqueoussolution. In contrast to Examples 1-7, where mixing is effectedcontinuously, Example 8 illustrates a batch operation of the processaccording to the invention.

EXAMPLE 1

An aqueous phase was prepared by dissolving 6.60 g of an aqueous pigmentdispersion containing 0.66 g of Pigment Blue 15:4 (BASF), 0.66 g ofT38909 dispersant (ethoxylated and sulfonated bisphenol A adduct ofstyrene, BASF), 0.22 g of humectant (1,2-propanediol, Merck) and 0.033 gof Proxcel preservative (1,2-benzisothiazoline compound, BASF) with 2000g of distilled water containing 0.66 g of a fluorosurfactant (Bayowet FT448, Bayer) in solution. A solvent phase was prepared by dissolving 2 gof a polycarbonate (Lexan 141, GE Plastics) and 1 g of Primacor 59801(copolymer of polyethylene and acrylic acid, DOW) in 200 g of THF.

The aqueous phase was continuously mixed at a flow rate of 507 g/minwith the solvent phase, flow rate 63.5 g/min. A rotary evaporator wasthen used at 45° C. and 90 mbar to remove the THF solvent and some ofthe water until a solids concentration of 3.1% by weight had beenreached.

The aqueous pigment dispersion thus obtained was analyzed using ananalytical ultracentrifuge. An H₂O/D₂O sedimentation analysis revealed auniform particle density of o=1.28±0.05 g/cm³. It is accordingly clearthat unitary core-sheath particles are present, i.e., that the pigmentparticles have been coated with polymer. The particle size wasdetermined by dynamic light scattering. It revealed a mean of 115 nm anda variance of 23%.

EXAMPLE 2

Example 1 was repeated except that Pigment Blue 15:4 was replaced by thesame amount of Pigment Red 122.

The flow rate was 505 g/min for the aqueous phase and 67 g/min for thesolvent phase. The sample was concentrated to a solids concentration of2.9%. The particle size was 136 nm coupled with a variance of 25%.

EXAMPLE 3

Example 1 was repeated except that Pigment Blue 15:4 was replaced by thesame amount of Pigment Yellow 138.

The flow rate was 491 g/min for the aqueous phase and 70 g/min for thesolvent phase. The sample was concentrated to a solids concentration of2.5%. The particle size was 194 nm coupled with a variance of 27%.

EXAMPLE 4

An aqueous phase was prepared by dissolving 36.6 g of an aqueous pigmentdispersion containing 3.66 g of Pigment Blue 15:4 (BASF), 3.66 g ofT38909 dispersant (ethoxylated and sulfonated bisphenol A adduct ofstyrene, BASF), 1.21 g of humectant (1,2-propanediol, Merck) and 0.18 gof Proxcel preservative (1,2-benzisothiazoline compound, BASF) with 11000 g of distilled water. A solvent phase was prepared by dissolving 23g of terpolymer (random copolymer of 20% styrene, 20% acrylic acid and60% 4-vinylpyridine) in 1533 g of acidic methanol consisting of 98% byweight of methanol and 2% by weight of 1 M HCl.

The aqueous phase was then continuously mixed at a flow rate of 510g/min with the solvent phase, flow rate 69 g/min. A rotary evaporatorwas then used at 45° C. and 90 mbar to remove methanol and some of thewater until a solids concentration of 4.0% by weight had been reached.The average particle size was 138 nm and the variance 20%.

EXAMPLE 5

An aqueous phase was prepared by dissolving 0.66 g of a fluorosurfactant(Bayowet FT 448, Bayer) in 2000 g of distilled water which had beenrendered slightly alkaline with 4 ml of 1 M NaOH. The solvent phaseconsisted of a solution of 2 g of a polycarbonate (Lexan 141, GEPlastics) and 1 g of Primacor 59801 (copolymer of polyethylene andacrylic acid, DOW) in 200 g of THF. Immediately prior to the continuousmixing of aqueous phase and solvent phase, 5 g of an aqueous pigmentdispersion containing 0.5 g of Pigment Blue 15:4 (BASF) and 0.5 g ofT38909 dispersant (ethoxylated and sulfonated bisphenol A adduct ofstyrene, BASF) were stirred into the solvent phase.

The aqueous phase was then continuously mixed at a flow rate of 500g/min with the solvent phase, flow rate 72 g/min. A rotary evaporatorwas then used at 45° C. and 90 mbar to remove the THF solvent and someof the water until a solids concentration of 4.0% by weight had beenreached. The average particle size was 252 nm and the variance 20%.

EXAMPLE 6

An aqueous phase was prepared by dissolving 6 g of a protective colloid(sodium caseinate, Lacto Bretagne Associés) and 5 g of afluorosurfactant (Bayowet FT 448, Bayer) in 14 000 g of distilled water.The pH was adjusted to 11.8 with 28 ml of 1 M NaOH. A solvent phase wasprepared by dispersing 4 g of Pigment Blue 15:3 (BASF) in 1600 g of THFusing 16 g of a polycarbonate (Lexan 141, GE Plastics) and 8 g ofPrimacor 59801 (copolymer of polyethylene and acrylic acid, DOW).

The aqueous phase was then continuously mixed at a flow rate of 507g/min with the solvent phase, flow rate 64 g/min. A rotary evaporatorwas then used at 45° C. and 90 mbar to remove the THF solvent and someof the water until a solids concentration of 7.8% by weight had beenreached. The average particle size was 262 nm and the variance 16%.

EXAMPLE 7

An aqueous phase was prepared by dissolving 0.66 g of a fluorosurfactant(Bayowet FT 448, Bayer) in 2000 g of distilled water which had beenrendered slightly alkaline with 4 ml of 1 M NaOH. A solvent phase wasprepared by dispersing 0.5 g of an SiO₂ pigment (Aerosil R 812, Degussa)in 200 g of THF using 2 g of a polycarbonate (Lexan 141, GE Plastics)and 1 g of Primacor 59801 (copolymer of polyethylene and acrylic acid,DOW).

The aqueous phase was then continuously mixed at a flow rate of 495g/min with the solvent phase, flow rate 71 g/min. A rotary vaporator wasthen used at 45° C. and 90 mbar to remove the THF solvent and some ofthe water until a solids concentration of 2.5% by weight had beenreached. The average particle size was 122 nm and the variance 24%.

EXAMPLE 8

An aqueous phase was prepared by dissolving 6.60 g of an aqueous pigmentdispersion containing 0.66 g of Pigment Blue 15:4 (BASF), 0.66 g ofT38909 dispersant (ethoxylated and sulfonated bisphenol A adduct ofstyrene, BASF), 0.22 g of humectant (1,2-propanediol, Merck) and 0.033 gof Proxcel preservative (1,2-benzisothiazoline compound, BASF) with 1500g of distilled water containing 0.66 g of a fluorosurfactant (Bayowet FT448, Bayer) in solution. A solvent phase was prepared by dissolving 2 gof a polycarbonate (Lexan 141, GE Plastics) and 1 g of Primacor 59801(copolymer of polyethylene and acrylic acid, DOW) in 397 g of THF.

The solvent phase was added dropwise, using a dropping funnel, over 100minutes with stirring.

The aqueous starting dispersion had an average particle size of 131 nmcoupled with a variance of 48%, whereas, after polymer coating of thepigment particles had been carried out, the particle size rose to 157 nmcoupled with a variance of 42%.

1. A process for preparing polymer-enrobed pigment particles, whichcomprises dissolving a polymer in a first solvent mixing the solution ofsaid polymer in said first solvent with a second solvent which containsfinely dispersed pigment particles and in which said polymer issubstantially insoluble, said second solvent being miscible with thefirst solvent, whereby said polymer is precipitated from the mixture ofsolvents onto said finely dispensed pigment particles wherein the firstsolvent is selected from organic water-miscible solvents.
 2. A processas claimed in claim 1, wherein the second solvent is water.
 3. A processas claimed in claim 1, wherein the polymer comprises a polyester, apolyvinyl acetal, polyacetal, polyurethane and/or a polyurea.
 4. Aprocess as claimed in claim 3, wherein said polymer comprises apolycarbonate.
 5. A process as claimed in claim 1, wherein the polymercomprises a polymer polymerized from 10-100% by weight of one or morewater-insoluble ethylenically unsaturated monomers, 0-90% by weight ofone or more water-soluble lethylenically unsaturated monomers and 0-30%by weight of one or more crosslinking monomers.
 6. A process as claimedin claim 1, wherein the first solvent and/or the second solventcontain(s) an emulsifier and/or a protective colloid in solution.
 7. Aprocess as claimed in claim 1, wherein the polymer has a glasstransition temperature of from −100 to +250° C.
 8. Pigmentarycomposition, suitable for use in an ink jet printing formulation,comprising composite particles of pigment from 10 nm to 500 nm in sizeand a polymer robe surrounding the pigment particle, said polymerenrobed pigment particles being made by the process of claim
 1. 9. Apigmentary composition of claim 8, wherein said polymer comprises apolyester, a polyvinyl acetal, polyacetal, polyurethane and/or apolyurea.
 10. A pigmentary composition of claim 8, wherein said polymeris comprised of from 10-100% by weight of one or more water-insolubleethylenically unsaturated monomers, 0-90% by weight of one or morewater-soluble ethylenically unsaturated monomers and 0-30% by weight ofone or more crosslinking monomers.
 11. A pigmentary composition of claim8, wherein said polymer comprises a polycarbonate.
 12. A pigmentarycomposition of claim 8, wherein said polymer comprises a mixture ofpolycarbonate and a copolymer of polyethylene and acrylic acid.
 13. Apigmentary composition as set forth in claim 8 wherein said polymercomprises a terpolymer of styrene, acrylic acid and 4-vinylpyridine. 14.A method of printing sheetlike substrates comprising ink jet printingsaid substrates with an ink jet ink comprising the pigmentarycomposition of claim
 13. 15. A method of printing sheetlike substratescomprising ink jet printing said substrate with an ink jet inkcomprising the pigmentary composition of claim
 8. 16. A process asclaimed in claim 1 wherein the solubility of said polymer in the secondsolvent is less than 1 g/l.
 17. A process as claimed in claim 1, whereinsaid polymer comprises a mixture of polycarbonate and a copolymer ofpolyethylene and acrylic acid.
 18. A process as claimed in claim 1,wherein said second solvent is water and said second solvent contains aprotective colloid.
 19. A process as claimed in claim 1, where thepolymer enrobed particles produced have an average particle size in therange of from 10 nm to 5 μm and a particle size distribution width(variance) of ≦60%.